The present invention relates to the conversion of acoustic signals, particularly audio signals, into visible information, according to a procedure in which the acoustic signals are divided in parallel connected filters and made visible on the screen of a cathode ray tube, and the brightness of the cathode beam in the tube is controlled in dependence on the intensity of the signals produced by the individual filters.
Many attempts have been made to overcome the lack of hearing capability of hearing impaired and deaf persons by converting acoustic signals, in particular audio signals, into a different form. Methods used in this connection include frequency transformation, vibration transmission to the skin, and optical conversions according to various "visible speech" methods.
For frequency transformation, the audio signals are transposed one or two octaves down because for most hearing impaired persons the hearing losses in the lower frequency ranges are not as severe as in the high audio frequency range.
However, this method, similar to vibration transmission to the skin, has not found great acceptance because the number of information elements that can be transferred per second is too low.
In a known "visible speech" method, described in the text "Einfuhrung in die Akustik" [Introduction to Acoustics] by Ferdinand Tredelenburg, 3rd revised edition, published by Springer-Verlag, Berlin, 1961, at pages 491, 492, sound spectrograms are displayed on the luminescent screen of a specially designed Braun tube. This tube is provided with a cylindrical luminescent screen which rotates past the observer about a vertical axis and on which impinges a cathode-ray coming from the middle of the cylinder. Alongside the vertical axis there is provided a frequency scale. The instaneous outputs from twelve filters divided by octaves are tapped in succession by a rotating switch. The brightness of the cathode beam moving over the vertical axis changes in accordance with the intensity of the outputs of the individual filters so that a sound spectrum is developed along this axis.
As the screen coated with a phosphorescent material rotates past the observer, he sees very clearly the intensity distribution of the sound pattern in question in the various regions of the spectrum and its variation in time. Time is plotted in the X, or circumferential, direction and frequency in the Y, or axial, direction, the degree of darkening of the screen indicating amplitude.
This type of signal conversion has gained great significance for voice recognition, for example, in criminal cases, but the information contained in the images can be evaluated only with the aid of very fine analysis methods so that such conversion has not found acceptance as a means of communication.